Ultrasonic guided wave techniques are utilized in a wide range of non-destructive inspection applications including those for pipes, plates, and shells comprised of metals, composites, and other materials. Guided waves are elastic waves propagating in a bounded structure that is utilized as a waveguide to efficiently transmit one or more wave modes along the structure. One of the foremost benefits of guided waves over other non-destructive inspection techniques is the ability of said waves to propagate over long distances, in many cases, hundreds of feet, and to inspect inaccessible or hidden structures from a single probe position.
Long-range guided wave techniques are often utilized for the inspection of pipelines; however, focusing-capable systems are often complex and costly due to the need for segmentation of the transducer collar. Segmentation allows the sound to be sent and received in a partial loading configuration around the circumference of the pipe. Partial receiving and, in some cases, partial loading are required to perform both active and synthetic focusing of guided wave energy in the pipe to identify the axial and circumferential location and extent of reflectors. Segmentation of the collar also makes it difficult for the transducer collars to provide axisymmetric loading, as the segmentation often leaves inactive zones between the segments. Conventional focusing-capable long-range guided wave pipeline inspection systems typically utilize complex multi-channel phased array pulser/receiver electronics capable of sending and receiving guided waves over many channels, typically 16-24, to support transducer collars arranged into 8 segments. In the case of synthetic focusing, it would be most ideal to send an axisymmetric wave and then be able to receive with partial loading. It would also be advantageous in some cases to be able to increase the number of receiving locations around the circumference of the pipe without having more channels in the pulser/receiver electronics and more segments in the transducer collar. It would further be advantageous to be able to have a system in which the aperture within the segments can be larger or smaller than the length of the circumference divided by the number of circumferential channels, which manifests as partial receiver section overlap.